Gas turbine components which are subject to high temperatures during operation of a gas turbine unit are for example the guide vanes and rotor blades of the turbine, wall sections of the turbine casing bounding the hot gas path through the turbine, and sections of the rotor bounding the hot gas path through the turbine. In order to increase the high-temperature strength of components, these are generally provided with a ceramic thermal barrier coating system which often consists of a ceramic thermal barrier coating and, below this, an adhesion-promoting layer, wherein the adhesion-promoting layer also serves for corrosion prevention and/or oxidation prevention. Thermal barrier coating systems of this kind make it possible to lower the temperature in the base material of the turbine components in comparison to the temperature at the surface of the coating system. In addition, in order to be able to reach even higher operating temperatures for the gas turbine unit, heat is removed from components subject to particularly high thermal load by passing cooling air through these components.
Methods for cooling a gas turbine are known for example from DE 102012011294 A1 or U.S. Pat. No. 5,611,197, both of which prescribe supplying compressor air via a cooling air path to components in the turbine section that are subject to high thermal load. After acting on the components in the turbine section, the cooling air is then passed back into a return line in order to be returned to the flow path in the compressor section. In this context, injection into the flow path takes place at a location upstream of the point at which the compressor air was originally taken.
However, components of the gas turbine unit which do not come into direct contact with the hot working medium in the flow path of the gas turbine, such as rotor sections located in the burner section of the gas turbine unit, are also exposed to high temperatures during operation of the gas turbine unit. Such components are also often cooled with cooling air. The air required for cooling the gas turbine components is taken from the compressor air at bleed points in the compressor of the gas turbine unit. After cooling of the gas turbine component to be cooled, the cooling air is supplied to the working medium in the hot gas path.
However, discharging the used cooling air into the hot gas path or into the flow path of the gas turbine unit influences both the aerodynamics in the hot gas path or in the flow path and the efficiency of the gas turbine unit. This is particularly true when—as is often the case nowadays—used cooling air is released at multiple locations into the flow path leading through the gas turbine unit.